This node group takes roughness into account when calculating Fresnel.
The group also has enhancements for roughness and color.
Grazing Reflectivity: This produces realistic reflections at grazing angles. The Grazing Reflectivity parameter controls the strength. The GR Falloff parameter extends the reflections.
Color Correction: This addresses an issue that causes color to appear too dark at grazing angles.
The group is compatible with 2.79 and 2.8.
Just to clarify, does a higher falloff extend or shorten the reflections?
I have also created a Grazing Reflectivity group for the Principled shader. https://www.blendswap.com/blend/23960